Device at artificial joints

ABSTRACT

Fastening means for artificial joints including two titanium wires that are wound into a spiral and wherein the wires clamp a number of bristles between them that extend essentially radially outwards towards the interior of the bone. The bristles are a little bit too long for undisturbed insertion into the cavity of the bone and, thus they will be slightly turned backwards on insertion, thereby securing a very steady grip once inserted.

BACKGROUND OF THE INVENTION

lt has been known for some time how to replace worn, or in other waysdamaged, joints--for instance joints damaged by rheumatism, by removinga joint end from a bone and replacing this end with an artificial part.These artificial parts include a joint part and a connection part thatis inserted into the cavity of the remaining bone. The fastening of theartificial part in the bone has been carried out in different ways, forinstance, the connection part has been threaded and/or cemented into thebone.

Presently available artificial parts have a number of drawbacks.Firstly, this method of fastening is comparatively complicated and timeconsuming. Secondly, with time, great loads, for instance in thevicinity of knee joints and thigh bones, cause an increasing playbetween an artificial part and bone, which may require a replacement ofthe artificial part. Change of the artificial part normally involves theshortening of the bone to obtain adequate material in which to fastenthe artificial part. After a few replacements of the artificial part, solittle of the bone remains that the joint must be made rigid due to thelack of bone material.

A further drawback of the artificial parts known thus far is that thenatural formation of blood vessels cannot occur within inner cavity ofthe bone, which presumably further reduces the life span of the mountingof the artificial part and, thus, of the artificial part itself.

SUMMARY OF THE INVENTION

Some objects of this invention are to solve the above mentioned problemsand to provide a simple, useable, artificial part fastening or mountingthat is easy to apply, that does not need to be exchanged, and thatallows improved vascularization. Other and further objects andadvantages will appear hereinafter.

These objects may be achieved in accordance with the present inventionby means of a supporting structure that is inserted into the axialcavity of the bone. This supporting structure is provided with bristles,fibers, loops, or the like, with such length that the combined diameterof the device is somewhat larger than the cavity in the bone, allowingat least some of the bristles, fibers, loops, or the like to retain acertain pretension at mounting. In other words, when the fasteningelement is inserted into the hollow of the bone, the bristles are bentsomewhat, thereby causing greater resistance against withdrawal thanagainst insertion. It will in fact be practically impossible to withdrawthe fastening element. Preferably the number of bristles, fibers or thelike is very large. In this way extensive contact between bone and theartificial part fastening element is obtained simultaneously as anadaption is automatically made to possible irregularities on the insideof the bone.

Furthermore, by fabricating the bristles, fibers, or loops in titanium,the bone and the artificial part fastening element will grow togetherand with time will become integrated. Bleeding and vascularization cantake place between the bristles, fibers or loops. Furthermore, it isalso possible to make the supporting structure more or less porous oropen. Since the tensions are less as you go further into the bone, thefastening element can be more open or have fewer bristles, furtherwithin the bone. The length of the bristles, and the density thereof,are primarily governed by the forces that have to be transferred.Therefore, the density of the bristles need not necessarily be the sameover the entire length of the fastening element.

If bristles of titanium are used, many thin bristles can be used in viewof the hard, stiff character of titanium. In the alternative,titanium-containing alloys coated by titanium can be used. It is alsopossible to use plastic materials coated with titanium.

The bristles may initially be directed radially or possibly somewhatrearward. It is also possible that only some of the bristles are sodirected.

The supporting structure need not necessarily be rigid, but may allow acertain elasticity that may preferably be calculated to coincide withthat of the bone so that no tension peaks are developed in the forcetransfer back and forth.

By means of the invention, an immediate sturdy grip is obtained in thebone, preventing the mounted artificial part from loosening. With theuse of titanium, the device is prevented from working loose over timesince the contact surface is great and, thus, the specific load small.

It should be observed that the fastening means described above can alsobe used for the joining of broken bones.

Further details and advantages of the invention will become apparentfrom the following description of a preferred embodiment and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a joint with the device of the presentinvention as seen from the front.

FIG. 2 shows the same joint and device of FIG. 1 in cross section fromthe side.

FIG. 3 shows a cross-section of a joint with an alternative embodimentof the device of the present invention from the side.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The artificial joint shown in the drawings (where like numbers designatelike elements) includes a bowl or concave joint part 4 and a ball jointpart 3, each fastened in a bone, 1 and 2 respectively. The lower part,the ball part 3, is welded to two wires 5 of titanium that, fromdiametrical peripheral fastening points, extend toward each other, thencontinue by winding around each other. In FIGS. 1 and 2, between thespirals of these two wires 5, thin threadlike bristles 6, also oftitanium, are clamped. FIG. 3 illustrated the use of loops 26 as analternative to the bristles 6 of FIGS. 1 and 2.

The bristles 6, or loops 26 are of a length such that they, on insertioninto the bone 2, will be bent somewhat upwards. This means that theywill not exert any particular resistance against their introduction intothe bone. However, the resistance against possible attempts to withdrawthe artificial joint part from the bone will be very great. By using alarge number of bristles or loops, a good fastening against turning ofthe artificial joint part relative to the bone is achieved.

The ball joint part 3 has a circumferential downwards protruding flange7 gripping around the bone 2 on its correspondingly shaped end 8. Inthis way, the artificial joint part will be locked against possibletilting, with the bristles and the titanium wire pressing the ball jointpart against the bone 2.

In one embodiment, the interior of the ball joint 3 can be filled withsilicone at the mounting. In the alternative, the interior can beentirely empty. By using pure titanium or titanium alloys or othermaterials coated with titanium, or perhaps even other materials that cangrow together with the bone, over time an integration is achieved. Inthis way, not only is there an immediate, sturdy attachment, but thereis also a lasting attachment to the bone.

The upper joint bowl part or concave part 4 has a shape corresponding tothe shape of the ball joint part 3 so that an angular movement ispossible. The surfaces facing each other are usually cylindrical orspherical surfaces where the lower ball joint part 3 has a waist orgroove 9 into which a protrusion or ridge 10 on the upper bowl jointpart can grip to provide an increased resistance against turning andsideways dislocation. By proportioning the interrelated length of grooveand the ridge angle, stops for the joint can be achieved. The upper bowljoint part 4 is not made of titanium, but is made of a syntheticmaterial that affords negligible friction against titanium. An exampleof this is high density polyethylene (HDP) that has proven to becompatible with human tissues. In the bowl part 4, a dove tail groove 12extends sideways and into this grips a correspondingly shaped dove tail14 that, in turn, is part of a titanium plate 13. Preferably, thetitanium plate 13 and the joint bowl part 4 of HDP are provided withsnap means so that the lateral location, when ideally situated, issecured. Wires 15 are welded to the plate 13 and are then wound to aspiral that holds bristles 16, or loops 28 in the same way as has beendescribed above for the lower ball shaped joint part 3. Also, thetitanium disk or plate 13 is provided with a flange 17 gripping around acorresponding shaping 18 of the bone 1.

The use of a dove tail joint to join the joint bowl part 4 with itsfastening means provides the advantage that the joint bowl part 4 caneasily be exchanged if, for instance, after many years of use, the partbecomes worn. The exchange can be accomplished through a procedure thatis far easier and less complicated and time consuming than would be thecase if it were necessary to exchange the entire artificial joint orartificial joint part.

Of course, the lower ball joint part 3 can also be made in a similar wayto allow a change of a part subjected to wear, as shown in FIG. 3. Thiscan, for instance, take place by use of a dove tail joint with theinterlocation of a plastic part. Thus, a dove tail groove 29 can extendsideways in the lower ball joint 3 and into this grips a correspondinglyshaped dove tail 22 that, in turn, is part of a plastic plate 24. Byusing plastic for one half of the joint, and possibly as a joiningelement in the lower part, a certain elasticity against shock isachieved that reduces tensions in other joints as well as in thefastening of the artificial joint.

It should be observed that the flanges 7 and 17, and the correspondingshaping of the bone ends respectively, need not necessarily be exactlymatched to the outer shape of the bone, but, instead, to facilitateworking, it is possible to use flanges that are circular, for instanceconcentric with the axis of the wound titanium wires.

The joint has a ligament 19 on each side.

By means of the invention, an artificial joint or joint parts isrealized for large as well as small joints that is very similar to thedesired relationships of the original joint.

Since the fastening according to the invention in principle is, or canbe made, elastic over its entire length, there will be no tension peakswhere the artificial part ends, unlike many known artificial joint partsin which such tension peaks do occur.

Due to the improved fastening characteristics and the soft transferenceof forces from the artificial part to the bone, it is actually possibleto make other types of replacements that have previously beenimpossible. Due to previously poor fastening characteristics, theartificial part has always had to be comparatively short in order toavoid having excessive torques exerted on the remaining bone part. Withthe invention, the remaining bone will not be subjected to forcesgreater than the bone originally could tolerate. Therefore, anartificial joint part according to the invention can be longer, therebyabolishing the previous necessity of bone shortening.

The drawings have shown the use of two wires for fastening the bristles.Of course, more than two wires can be used and it is also possible touse different types of supporting structure for carrying the bristles.For instance, the bristles can be fastened in a cast plastic structure.

If the stiffness of the supporting structure decreases towards theinterior of the cavity, the transference of forces to and from the jointwill take place without significant tension peaks.

In the above example, two wires have been used to secure or fasten thebristles, however, a greater number of bristles can also be used.Furthermore, if any other type of supporting structure is used, forinstance a plastic structure, then a porous or open structure can alsobe employed.

Thus, a fastening means for artificial joints is disclosed. Whileembodiments and applications of this invention have been shown anddescribed, it would be apparent to those of ordinary skill in the artthat many more modifications are possible without departing from theinventive concepts herein. The invention, therefore, is not to berestricted except in the spirit of the appended claims.

What is claimed is:
 1. An artificial joint for connecting an upper bonehaving a cavity therein and a lower bone having a cavity therein, saidartifical joint comprising:an upper concave joint part having a concaveportion and an opposite side; a lower ball joint part having a roundedportion and an opposite side oriented such that the rounded portion ofthe lower ball joint part fits within the concave portion of the upperconcave joint part; a pair of support structures, one attached to theopposite side of the upper concave joint part and one attached to theopposite side of the lower ball joint part, each of the supportstructures having an end remote from their respective joint partsadapted for insertion and retention into a cavity of one of said upperand lower bones and holding means on each support structure for holdingsuch support structure in a respective bone cavity, said holding meanscomprising a plurality of bristles, fibers, or loops extending from arespective structure only radially outwardly and toward a respectivejoint part, wherein the length of at least a portion of the bristles,fibers, or loops is such that an outer diameter of such bristles,fibers, or loops as attached to the respective support structures in anuntensioned state is adapted to exceed the diameter of the cavity inwhich it is to be inserted.
 2. The artificial joint of claim 1 whereineach of said support structures comprise a spiral of wound wires, saidbristle, fibers, or loops being clamped between the wound wires.
 3. Theartificial joint of claim 1 wherein one or more of the lower ball jointpart, the support structures, and the bristles, fibers, or loops arecomprised of titanium or titanium alloys.
 4. The artificial joint ofclaim 1 wherein one or more of the lower ball joint part, the supportstructures, and the bristles, fibers, or loops are coated with titanium.5. The artificial joint of claim 1 wherein the density of the brrstles,fibers, or loops decreases towards the remote ends of the supportstructures
 6. The artificial joint of claim wherein said supportstructures are comprised of a plastic.
 7. The artificial joint of claimwherein said support structures decrease in stiffness towards the remoteends inserted into the bone cavities.
 8. The artificial joint of claim 1wherein the rounded portion of the lower ball joint part has a grooveinto which a protrusion on the concave portion of the upper concavejoint part fits to provide increased resistance against turning andsideways dislocation of the attached bones.
 9. The artificial joint ofclaim 1 wherein the upper concave joint part is comprised of a cup parthaving a concave side and an opposite side and a plate part attached tosaid opposite side of the cup part.
 10. The artificial joint of claim 9wherein the cup part of the upper concave joint part is comprised of abiocompatible material chosen to minimize friction with titanium. 11.The artificial joint of claim 9 wherein said cup part of the upperconcave joint part is comprised of high density polyethylene.
 12. Theartificial joint of of claim 9 wherein said plate part of the upperconcave joint part further comprises a flange extending away from thecup part and formed to grip the upper bone.
 13. The artificial joint ofclaim 9 wherein said plate part of the upper concave joint part iscomprised of titanium or titanium alloys.
 14. The artificial joint ofclaim 9 wherein said plate part of the upper concave joint part isremovably attached to the cup part to allow replacement of the said cuppart.
 15. The artificial joint of claim 14 wherein said plate part isremovably attached by means of a dove tail ridge extending along saidplate part in a direction perpendicular to the bending plane of saidartificial joint that is inserted into a dove tail groove extendingalong the opposite side of said cup part in a similar direction
 16. Theartificial joint of claim 1 wherein said lower ball joint part furthercomprises a flange extending from the opposite side and formed to gripthe lower bone.
 17. The artificial joint of claim 1 wherein said lowerball joint part is comprised of a rotator part having a rounded portionand an opposite side and a plate part attached to the opposite side ofthe rotator part.
 18. The artificial joint of claim 17 wherein saidplate part of said lower ball joint part is comprised of an elasticsubstance.
 19. The artificial joint of claim 17 wherein said plate partof the lower ball joint part is removably attached to the rotator partto allow replacement of the said rotator part.
 20. The artificial jointof claim 19 wherein said plate part of the lower ball joint part isremovably attached by I0 means of a dove tail ridge extending along saidplate part in a direction perpendicular to the bending plane of saidartificial joint that is inserted into a dove tail groove extendingalong the opposite side of said rotator part in a similar direction. 21.An artificial joint for connecting an upper bone having a cavity thereinand a lower bone having a cavity therein, said artificial jointcomprising:an upper concave joint part comprised of a cup part, having aconcave side with a protrusion therein and an opposite side, and a platepart removably attached to said opposite side of said cup part; a lowerball joint part having a rotator part having a rounded portion with agroove therein and an opposite side, oriented such that the roundedportion of the lower ball joint part fits within the concave portion ofthe upper cancave joint part and the groove fits to the protrusion, anda plate part removably attached to the opposite side of the rotatorpart; a pair of support structures, each comprised of a spiral of woundwires, one attached to the opposite side of the upper concave joint partand one attached to the opposite side of the lower ball joint part, eachof the support structures having an end adapted for insertion andretention into a cavity of one of said upper and lower bones and holdingmeans on each support structure for holding such support structure in arespective bone cavity, said holding means comprising a plurality ofbristles, fibers, or loops extending from a respective structure onlyradially outwardly and toward a respective joint part, the length of thebristles, fibers, or loops being such that an outer diameter of thebristles, fibers, or loops as attached to the support structure in anuntensioned state is adapted to exceed the diameter of the cavity inwhich it is to be inserted and the bristles, fibers, or loops are angledonly radially downwardly from the support structure towards the jointparts and we adapted to be tensioned against the interior of thecavities; and wherein one or more of the plate part of the upper concavejoint part, the rotator part, the plate part of the lower ball jointpart, the wound wires, and the bristles, fibers, or loops is comprisedof titanium or titanium alloys.